I. Field of the Invention
This invention relates to porous membranes made of sintered refractory metal oxides, e.g. alumina, titania, zirconia, tungsten oxide, and silica, and to a process for forming such membranes.
II. Description of the Prior Art
Thin porous membranes made of high temperature-resistant ceramic materials, such as those mentioned above, are useful for a variety of purposes. For example, they may be used as high temperature filters or as catalyst supports. Sintered products of this type can be produced by heating, to the sintering temperature, a shaped product made of particles of the ceramic material loosely held together. However, it is often difficult to control the porosity of the products by such procedures and thin membranes are difficult to produce because the product is subject to cracking.
Ceramic membranes with micron sized pores are most commonly prepared by sol-gel techniques, e.g. as disclosed in Futuretech, 38, July 27, 1987, p 9 (published by Technical Insights, Inc., Englewood, NJ, USA). Another method of making membranes having angstrom sized pores is by anodic oxidation of aluminum or aluminum alloys, e.g. as disclosed in Japanese published patent application (Kokai) No. 61 71804 to Toyo Soda Mfg. Co. Ltd. of April 12, 1986 and in Japanese published patent application (Kokai) No. 60 177,198 to Nippon Sheet Glass Co. Ltd. of September 11, 1985.